2017-01-18 07:11, Jay Rolette: > On Wed, Jan 18, 2017 at 5:05 AM, Sergey Vyazmitinov < > s.vyazmiti...@brain4net.com> wrote: > > > On Thu, Jan 12, 2017 at 12:29 AM, Ferruh Yigit <ferruh.yi...@intel.com> > > wrote: > > > > > On 12/29/2016 11:23 PM, Sergey Vyazmitinov wrote: > > > > This allow to significant reduces packets processing latency. > > > > > > > > Signed-off-by: Sergey Vyazmitinov <s.vyazmiti...@brain4net.com> [...] > > > > --- a/lib/librte_eal/linuxapp/kni/kni_misc.c > > > > +++ b/lib/librte_eal/linuxapp/kni/kni_misc.c > > > > @@ -45,6 +45,7 @@ MODULE_AUTHOR("Intel Corporation"); > > > > MODULE_DESCRIPTION("Kernel Module for managing kni devices"); > > > > > > > > #define KNI_RX_LOOP_NUM 1000 > > > > +#define KNI_RX_DATA_LOOP_NUM 2500 > > > > > > > > #define KNI_MAX_DEVICES 32 > > > > > > > > @@ -129,25 +130,39 @@ static struct pernet_operations kni_net_ops = { > > > > #endif > > > > }; > > > > > > > > -static int > > > > -kni_thread_single(void *data) > > > > +static inline void > > > > +kni_thread_single_rx_data_loop(struct kni_net *knet) > > > > { > > > > - struct kni_net *knet = data; > > > > - int j; > > > > struct kni_dev *dev; > > > > + int i; > > > > > > > > - while (!kthread_should_stop()) { > > > > - down_read(&knet->kni_list_lock); > > > > - for (j = 0; j < KNI_RX_LOOP_NUM; j++) { > > > > - list_for_each_entry(dev, &knet->kni_list_head, > > > list) { > > > > + for (i = 0; i < KNI_RX_DATA_LOOP_NUM; ++i) { > > > > > > When there are multiple KNI interfaces, and lets assume there is traffic > > > too, this will behave like: > > > > > > KNI1x2500 data_packets + KNI2x2500 data_packets .... KNI10x2500 > > > > > > After data packets, KNI1 resp_packet + KNI2 resp_packets ... > > > > > > Won't this scenario also may cause latency? And perhaps jitter according > > > KNI interface traffic loads? > > > > > > This may be good for some use cases, but not sure if this is good for > > all. > > > > > We can decrease KNI_RX_DATA_LOOP_NUM to some reasonable value. > > I can make test to find lower bound. > > Also, the point is in fast check for a new data in interface rx queue. > > May be will be better add some kind of break after several kni_net_rx > > calls. > > Without them loop ends very quickly. > > Anyway, this patch decrease average latency in my case from 4.5ms to > > 0.011ms in ping test with 100000 packets. > > > > If you were seeing latency of 4.5ms, then it is more likely a different > issue. > > At the end of the loop where KNI is reading packets from the queue, it > calls *schedule_timeout_interruptible()* with (by default) a 5us timeout. > However, that call just guarantees that the thread will sleep for AT LEAST > 5us. > > For most x86 Linux distros, HZ = 250 in the kernel, which works out to 4ms. > I'm reasonably certain the latency you are seeing is because the KNI thread > is sleeping and not getting woken up like you might expect. > > When you increased the number of loops happening before the sleep, you > increased how long KNI spends before it sleeps and it happened to be long > enough in your particular test to change your average latency. If you ran > your test for a few minutes and built a histogram of ping times, I bet > you'll see ~4ms of latency pop up regularly. > > More details from when I dug into this behavior previously: > http://dpdk.org/ml/archives/dev/2015-June/018858.html
No answer in this discussion. Should we close it in patchwork?